Rock bolts are common throughout the world and are typically drilled into strata and retained therein to provide support to the integrity of the strata which assists with supporting structures. For example, rock bolts can be used in the construction and maintenance of mines, tunnels, passageways, canals, enclosures, shafts, halls, access ways, subways or the like.
In underground tunneling, for example, rock bolts are often installed at progressive intervals along the tunnel. During the construction of the tunnel it is desirable to provide a rock bolt that is easy to secure into the strata with the least human intervention due to the highly hazardous environment.
The most common method of securing a rock bolt to strata is to drill a hole in the strata using a drill rig with a drill rod. Once the hole has been bored and the drill rod is retracted from the hole, the drill rod is removed from the drill chuck. A bolt is then inserted into a drive dolly which is an adapter between the bolt and drive chuck. A resin capsule is then inserted into the bored hole. The bolt is then inserted into the bore hole causing the resin capsule to rupture. The bolt is then rotated to promote mixing and dispersion of the resin. Once the resin has set, a nut on the end of the bolt is rotated and the nut comes into contact with the collar of the hole. Torque is applied to the nut on contact with the collar of the borehole and the nut places tension over the length of the bolt that has not been already anchored to the strata. As a result, the strata is then placed in compression, containing the strata.
The above described bolting method has many steps and involves a high level of manual handling. Repetitive manual handling tasks of this type ultimately lead to accidents and injuries. The speed of installation of a bolt is governed by the proficiency of the operator, and this can vary considerably. Production demands require an efficient installation time for strata support, however, this method takes time due to the many steps involved.
Self-drilling rock bolts were developed to overcome the above disadvantages. They are known for providing a single drilling and securing function. This negates the need to drill a hole, withdraw the drill rod and subsequently insert a bolt into the hole using various methods of anchoring.
Hollow, steel, self drilling rock bolt versions have been developed to minimize the number of cycles involved when rock bolting strata. One self drilling rock bolt utilizes the centre hole of the bolt as the delivery port for water during the drilling process as well as an avenue to pump cement grouts and resins of various sorts to anchor and encapsulate the bolt. The self drilling rock bolt is then simply filled both internally and externally about the bolt annulus, and therefore provide a dowel support to the strata. No tension is applied to the length of the bolt in the strata.
Mechanically anchored self drilling rock bolts are also available. They can be used in combination with cement grouts or resins that are inserted post anchoring with the mechanical anchor. However, the mechanical anchor technique can also fail when the surrounding borehole strata is weak and is unable to provide sufficient resistance to allow tensioning. The bolt is heavier than alternate options and the system is also slow due to the post grouting step for full encapsulation.
Another self-drilling rock bolt system utilizes a hollow bar with a chemical resin capsule already placed in the centre of the bar. Water is used as the drill and flush medium and travels through the middle of the bolt. Once the hole is drilled using the bolt, water is delivered into the cavity of the bolt containing the resin capsule. The water forces the resin capsule to disperse and mix before flowing around the annulus of the bolt. When the chemical resin has set, the bolt has reinforced the strata in the form of a dowel. The disadvantage of this system is that the bolt is very expensive to manufacture due to the internal arrangements within the bolt. Also, each bolt then has a shelf life based on the resin cartridge expiration.
In addition to the above disadvantages, existing self-drilling rock bolts, though used throughout the world, are expensive, time consuming to install, heavy, cumbersome and complicated to install correctly. Also full automation has not yet been achieved for installing traditional self-drilling rock bolts. Mechanical anchors, static mixers, individual chemicals, springs and the like also make known self-drilling rock bolt systems non automatable. Mechanical anchors in soft strata conditions can also fail and therefore won't allow the bolt to be pre-tensioned.
It is beneficial to apply pre-tension to an installed rock bolt to provide greater resistance to any strata movement. This can be accomplished by applying tension to the rock bolt once it has been secured to the strata by the hardening substance for a predetermined distance along the bolt effectively straining the bolt longitudinally, and then securing the rock bolt in tension using the nut and thread against the drill hole collar.
Accordingly, there is a need to provide a rock bolt drill head mechanism, a self-drilling rock bolt, a fluid delivery system and a method for securing the self-drilling rock bolt to strata that separately (or together) provides that the strata is supported quickly, reliably and efficiently, increases worker safety, provides significant automation, can be pre-tensioned, provides a multi-use injection system for use with multiple substances, reduces costs, provides productivity improvements and reduces the amount of human intervention and hence improves safety at an operation site.